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Key Clinical Questions

  • image Which patients with tickborne diseases should be hospitalized?

  • image How are Lyme disease, babesiosis, ehrlichiosis, anaplasmosis, and Rocky Mountain spotted fever diagnosed and treated?

  • image When should tickborne encephalitis be suspected?

  • image What are the clinical features of infection with the newly described pathogen Babesia miyamoti?


Poor land management prior to the 1920s resulted in massive deforestation in the Northeastern and upper Midwestern United States. The conservation movement and the decline in small family farms in these parts of the country have led to the return of forest and meadow land. With reforestation has come the large scale recovery of deer and other mammals, making for conditions in which Lyme disease and other tickborne illnesses can thrive. Since it was first described in 1977 in Lyme, Connecticut, Lyme disease has become the most common vectorborne disease in the United States. In 2013, the Centers for Disease Control and Prevention (CDC) reported over 36,000 confirmed or probable cases in the United States, with 95% of cases occurring along the eastern seaboard from Virginia to Maine, as well as in the upper Midwest states of Minnesota and Wisconsin.

Lyme disease is caused by the organism Borrelia burgdorferi, a spirochete, or corkscrew-shaped bacterium. The life cycle of this organism includes both invertebrate (tick) and vertebrate (mammalian) hosts. The major tick vector for Lyme disease in the United States is Ixodes scapularis, with Ixodes pacificus ticks transmitting the disease in areas along the West Coast. There is no transovarian spread of B. burgdorferi; ticks are not infected when they are hatched from eggs. Ticks must take a blood meal during each of its life stages (larvae, nymph, and adult), and acquire infection by feeding on an infected mammalian host.

The vast majority of Lyme disease cases are reported from May through August, but ticks may forage at any time the weather is warm enough for them to be active. A good rule of thumb is that if it is warm enough not to need gloves on while out of doors, it is warm enough for ticks to forage.


Lyme disease may usually be managed as an outpatient. However, there may be patients with acute complications which require hospitalization. These include those with meningitis, high-degree atrioventricular (AV) block, and systemic illness with possible coinfection with Anaplasma, Ehrlichia, or Babesia species.


Lyme disease is often described as having three distinct phases: early localized disease, early disseminated disease, and late Lyme disease. This is a useful framework, but in reality Lyme may be more of a disease continuum, as there is often significant overlap of many features.

Early localized disease (Table 199-1). Patients with acute B. burgdorferi infection may experience a wide ...

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